1. Technical Field
This disclosure relates generally to pumps and more particularly to seal assemblies for centrifugal pumps which may for example be for handling abrasive materials such as for example slurries and the like.
2. Background Art
Conventional centrifugal pumps have a seal assembly that provides a seal between the pump shaft and the pump casing. Many types of the seal assemblies are employed for such use. One typical type is a gland seal assembly which comprises a housing which is also referred to as a stuffing box. The gland seal assembly typically has a cylindrical bore through which the pump shaft passes. An annular gap is provided between the cylindrical bore and the pump shaft for receipt of packing material. One type of packing material may be in the form of a number of packing rings which are formed of any suitable packing material, depending upon the application.
The packing material is normally placed into the housing or stuffing box and compressed from the outside end by a gland. Due to the compressibility of the packing this allows the gap between the packing and shaft to be adjusted by moving the gland into and out of the annular gap forming a packing space. External bolts normally permit this adjustment to be effected.
Slurry pumps present a particular problem with respect to gland seal assemblies because the slurry being pumped contains particles. These particles cause additional friction and wear to the packing and sleeve. For slurry pumps it is common practice to inject water from an external supply into the assembly to reduce these problems and ensure a long life. The water is injected into the assembly via a feed channel to a lantern ring assembly. The lantern ring assembly may comprise a lantern ring and a restrictor or throttling bush. The lantern ring and restrictor direct the water introduced via the channel into a gap around the shaft. This allows water into the gap between the packing and the shaft for proper and effective lubrication, and has the effect of flushing solids or particles away from the seal assembly.
Injecting water into the seal assembly can cause dilution of pump fluid which can increase the cost of downstream processing such as dewatering. Water that leaks out the atmosphere side of the pump normally just flows to waste and can become an environmental problem. The throttling bush or restrictor limits the water flow into the pump, and the packings are used to limit the flow to the atmospheric side. These throttling parts are used mainly because of relatively large clearances between the housing and the shaft due to manufacturing tolerances. In typical use, the shaft does not run truly orthogonal to the stuffing box wall. Furthermore the current seal assemblies are relatively complex.
Another problem concerns lifting the seal assembly into position which can be difficult, as it needs to be placed to fit against components on its outside and inside diameters and also on its rear face. The front face is normally the only face that can be used for lifting.
The current arrangement for lifting seal assemblies involves soft metal inserts being cast into the hard metal casting of the stuffing box, the soft metal inserts are drilled and tapped. The stuffing box has these holes plugged with bolts in service and, when required to be installed or removed from a pump, the bolts are removed and a lifting tool is bolted onto the stuffing box. The soft inserts become a wear point in the hard metal stuffing box in service, and the bolts often wear away, making it difficult to remove them or, in a worst case, the tapped thread actually wears and the lifting tool cannot be attached. The soft metal inserts reduce the wear life of the stuffing box.